quiz 2 Flashcards
what are the two types of coordinate systems
- Cartesian coordinate system
- Polar coordinate system
what is a map projection and what are the two elements of map projections
Project a round globe onto a flat surface
1.) projective surface
2.)perspective point
what are the three map projection surfaces
1.)Cylindrical
2.)Conical
3.)Planar
What are the three map projection viewpoints
Gnomonic – Earth center
Stereographic – Earth Surface
Orthographic – infinity
where is the view point on a gnomonic viewpoint
Earth center
where is the view point on a Stereographic viewpoint
Earth Surface
where is the view point on a Orthographic viewpoint
infinity
What are the four properties of map projection and how many can be kept
you can only keep 2 and the four properties are
– Area (equal-area or equivalent)
– Shape (conformal or orthomorphic)
– Distance (equidistant)
– Direction (azimuthal or zenithal)
What is preserved and not in a cylindrical projections
Shapes are preserved
But not area or bearings or distances
what type of projection is mercator
cylindrical
what are conic projections best for
Best for hemispheres
or small regions
what type of projection is lamber
conic
what distortions does conic projection have and what does it keep
Distortions
–Distance?
* Yes
–Areas?
* No
–Bearings?
* Yes
what are planar projections good for
Good for one hemisphere
what are the types of planar projections?
- Gnomonic projection
- Stereographic projection
- Orthographic projection
what are the distortions and what is kept on a planar projection
- Distortions
–Distance? - Yes
–Areas? - Yes
–Bearings? - No
what are the pros and cons of UTM
- Advantage
– Minimal Distortion - Disadvantage
– Multiple zones
what is a datum
Datum - formal description of the Earth surface
what is a geodetic datum and what are its two parts
- Geodetic datum - reference system describing
Earth’s surface. - Geodetic datum contains two parts:
– Shape of the Earth: ellipsoid (geoid)
– Reference points and axis against which
measurements are made
what is nad 83
- North America Datum - NAD 83
– Replaces NAD 27 datum - Initial point in Kansas: Meades Ranch Station
– Based on ellipsoid
– Geocentric
– Suited for the entire planet
what is WGS 84
- World Geodetic System 84 - WGS 84
– Standard use in cartography, geodesy, and GPS
– Based on the same ellipsoid as NAD83 (GRS80)
– Coordinate system origin: Earth’s center of mass
What are the segments of GPS
1.)control
2.)Space
3.)User
How many satellites do we need for GPS
four for trilateration
what are the 5 GPS errors
- The errors experienced by the GPS users:
1. Satellite clock-they are not perfect
2. Satellite orbit-
3. Atmospheric delays
4. Multipath-Signal delay due to scattering off objects on earth
5. Receiver clock
What is a PDOP?
Position Dilution of Precision- basically the further spread out satellites are the better your location will be
How can we improve the accuracy of our GPS measurements? 3 ways
- Solution wait for better acquisition (not very practicable)
- Solution: Differential GPS (DGPS)
Post processing of location using GPS
3.)Real Time Kinematics GPS:Measure the phase of the signal’s carrier wave in addition to other information
what are the pros of aerial photography
Advantages
– Improved vantage point
– Capability to stop action
– Permanent recording
– Broader spectral sensitivity
– Increased spatial resolution
– Increased geometric fidelity
what is focus and what does it depend on
- The process of adjusting the lens to achieve
maximum sharpness to the chosen subject - Focus depends on:
1. Focal length of the lens, f
distance from lens at which parallel light rays are focused to a point
2. Distance between lens and object, o
3. Distance between lens and image plane, i
what is f-stop
f-stop - diameter of the lens opening of a camera
f-stop number increases = diameter of the lens opening decreases→ image exposure decreases
what are the advantages of digital images
Enhanced image capture capabilities
– sensitivity (response to reduce amount of radiation)
– linearity (response to amount of radiation)
– dynamic range (difference between darkest & lightest)
* Reduced time and complexity of creating primary
products
* Intrinsic compatibility with digital technologies
why can we not measure an oblique photo
because stuff in the foreground middleground and background are all different sizes and distances away because of the angle at which the photo is taken.
what are the types of aerial photography and do all images have tilt>?
- Type of aerial photos
– Vertical
– Oblique - All images are tilted, even the vertical ones
what is the nadir line
Nadir line - line on the ground directly
beneath the aircraft during photo acquisition
what is the zenith line
zenith is the line that points up from the earths sufrace while nadir points down
what is Stereopsis
- Stereopsis - the perception of depth and 3D obtained from visual information of two eyes
- Forward Overlapping with more than 50%
essential for stereoscopic coverage-usually 60% - Air base – ground distance between centers of two successive photo
- Side overlap of ≈30%
what is a photoscale
Photograph scale: one unit of distance on the photo represents a specific number of units in reality
what are the two types of displacement
- Tilt displacement
* Caused by a tilt of the image - Terrain displacement
* Caused by terrain morphology
what is tilt displacement
Tilt displacement - the shift
in an object’s image position
on a tilted photo from its
position on a vertical photo.
what is relief displacement
Relief displacement - the
shift in an object’s image
position caused by its
elevation above datum.
